This invention relates generally to ventilated cage and rack system, and more particularly to an open rack system which maximizes both cage density within the rack and useful volume within each cage while providing protection for both personnel attending to the system and animals contained within the cages from contamination.
Ventilated cage and rack systems are well known in the art. One such ventilated cage and rack system is disclosed in U.S. Pat. No. 4,989,545, assigned to Lab Products, Inc., in which an open rack system including a plurality of shelves, each formed as an air plenum, is provided. Air ventilation is provided directly to animals within each cage by allowing air to travel within each shelf to a plurality of predetermined positions within the rack. At least one cage level barrier having a filter bonnet is positioned on a shelf, so that the shelf removes air disposed adjacent the bonnet. A cage guide is formed in substantially the same shape as the bonnet and is affixed to the bottom of the shelf so that when the barrier cage is placed within the ventilated rack, it is positioned within the cage guide. The cage guide is separated from the bonnet by a relatively small distance. The air plenum shelf is provided with a negative pressure to remove gases from above the cage bonnet.
The prior art ventilated cage and rack system was satisfactory. However, because each shelf acted as an air plenum, each shelf required a certain height within the rack to allow for air to travel therethrough. Accordingly, the combined height of each shelf and the cage guides mounted below each shelf limited the vertical stacking density of cages within the rack because each row of cages was vertically separated from adjacent rows in the rack by at least this combined height.
Filter caps for animal cages used within ventilated cage and rack systems are also well known in the art. One such filter cap is disclosed in U.S. Pat. No. 4,640,228, assigned to Lab Products, Inc., in which a cap body with a perforated top wall is provided. A sheet of filter material is sandwiched between a retainer and the lower surface of the perforated top wall of the cap body. The retainer is detachably mounted inside the cap body in flush abutment with the filter material placed against the lower surface of the top wall of the cap body. The retainer comprises a narrow border portion and flat cross arms which intersect at an integral central portion.
This prior art filter cap was satisfactory. However, because the retainer was secured to the cap body on the interior of the cap body, changing a filter with an animal within the cage was inhibited because the entire filter cap required removal from the cage to remove the retainer and change the filter. Moreover, because the retainer was substantially open, the bottom side of the filter was substantially exposed to animals within the cage who might damage the filter, rendering it ineffective and resulting in contamination or requiring additional structure such as a wire bar lid for protection of the filter.
Another such filter cap is disclosed in U.S. Pat. No. 4,480,587, assigned to Lab Products, Inc., in which a cap body with an open top portion provided with a ledge and cross arms is provided. A filter is detachably secured to the cap body by an overlaying protective plate member which is fastened over the ledge and cross arms using a plurality of fasteners, such as threaded bolts which pass through holes in the plate member, filter and cap body and secured by respective nuts.
This prior art filter cap was also satisfactory. However, because separate fasteners were used to mount the protective plate to the cap body, personnel changing a filter were required to use special tools to remove the protective plate to release the filter. The use of such tools required additional resources and was time-consuming. Moreover, because the cap body had a substantially open top, the bottom side of the filter in this design was also unprotected from animals within the who might damage the filter and render it ineffective. In addition, the substantially open top inhibited changing a filter with an animal within the cage because of the possibility that the animal could escape through the open top.
Typically, the cages in a rack system must be removable from the rack system to provide access to the animals for feeding and testing, and to the cages for cleaning, maintenance and transport. However, it also required that the rack air source and/or water source mate with the cage to provide air and water to the cage. To accommodate this requirement it is known in the art to provide a structure so that the valve in each cage is connected to an air and/or water plenum on the rack by a coupling system. In such a system, each cage is connected to the plenum by pushing the cage into a rack until the coupling at the rear of the cage is connected to the coupling provided on the plenum. The couplings are disengaged by simply pulling the cage out of the rack, which closes a valve within the plenum coupling to prevent the escape and contamination of water and air. One such system is disclosed in U.S. Pat. No. 5,042,429, assigned to Lab Products, Inc. These prior art animal cage rack systems provide a friction fitting to maintain the connection between the couplings. These couplings have been satisfactory. However, they suffer from the disadvantage that, if the cage is not properly installed in the rack or is accidentally bumped during use, the couplings may become partially or wholly disengaged. In such an event, the water valve may be stuck open, flooding the cage.
Locking mechanisms have been designed to prevent a cage from being accidentally uncoupled from the plenum once the cage is properly installed. However, these prior art designs have been large, cumbersome and expensive. Moreover, modem cage and rack systems must allow cages of various lengths to be accommodated within the rack. The locking mechanisms of the prior art do not easily permit the secure locking of cages of various lengths within the rack.
Accordingly, it is desired to provide a ventilated cage and rack system which maximizes the stacking density of cages within the rack. It is also desired to provide a filter cap for animal cages used in a ventilated cage and rack system which permits easy changing of the filter while an animal is within the cage and which protects the filter in use from damage caused by the animal. It is further desired to provide a simple animal cage rack locking mechanism which enables an operator to lock cages of various lengths within a rack.